For Sunday, Oct 10, I am looking at Trainline only because it seems easier for me to understand.
It looks like going from Nice at the City Station (vs TGV station at airport) to Aix en Provence (to TGV station) is at 6 a.m. This train has no change in Marseilles, is cheaper, takes less time, BUT is really too early for me to be hanging around a train station by myself.
A better option looks like one at 7:57 a.m. from Nice Ville TGV Inoui with change in Marseilles to Aix en Provence city center via a TER train.
French train experts, please let me know if you agree with my thinking on above connection or suggest a different route. Price is about $56 and journey length is about 3 hr & 45 min.
Any problems about changing trains in Marseilles?
October 10 is a Tuesday. Please check your travel date.
Aix en Provence TGV station is 10 miles from Aix: you would need to take the bus from there. Changing in Marseille for a train to central Aix will be just as convenient, and the time is much better.
Edited to add that there are no steps to navigate at Marseille Saint Charles station. And if for some reason there is an issue with trains from Marseille to Aix, there are buses leaving every 5-15 minutes from the bus station which shares the same building as the train station.
Thanks, acraven. Yes, I meant Sunday October 8 from Nice to Aix.
Thanks, Balso, especially for the additional comments.